Automatic transmissions have been established in the automotive industry as a major way to transmit power from an internal combustion engine to wheels of an automobile with a torque and angular velocity which drives the automobile in a manner desired by the vehicle operator. The primary advantage of the automatic transmission over a manual transmission is that the automatic transmission relieves the vehicle operator from the requirement of manually shifting gears and operating a clutch while driving the vehicle.
While there are various nuances to automatic transmission operation, this application is concerned primarily only with a modification to existing automatic transmissions. Thus, details of automatic transmission structure and operation are omitted to the extent that they do not directly affect a thorough explanation of the invention described herein.
Automatic transmissions have often exhibited failure rates which are more frequent than failure rates of other types of transmissions. Furthermore, as a general rule, the repair costs involved in automatic transmission failures have exceeded the cost of repair for other types of transmissions. One common source of automatic transmission failure is through blowout of check balls located within clutch drums of the automatic transmission. (Clutch drums are also referred to as clutch liners in some publications).
One fairly common configuration of an automatic transmission (exhibited for example in the turbo hydro-matic 350 automatic transmission manufactured by General Motors) including a clutch drum having a hole passing therethrough with a check ball located within the hole. The hole is staked on an end adjacent a clutch piston to prevent the ball from exiting the hole. The hole and check ball are provided so that hydraulic fluid can enter a small gap between the clutch piston and the clutch drum but can not escape through the same hole. When the hydraulic pressure is of a sufficient value, the hydraulic fluid can cause the clutch piston to move away from the clutch drum. The net effect is to apply the clutch and cause the automatic transmission to shift to a different gear ratio.
In this check ball configuration, the automatic transmission often fails by having the staked portion of the clutch drum break away allowing the check ball to enter the region between the clutch drum and the clutch piston. The tight clearances and high rotational velocities of the clutch drum and clutch piston allow the clutch ball to severely damage the clutch drum and the clutch piston. Furthermore, without the check ball in place hydraulic pressure cannot be maintained on the clutch piston and so at least one gear of the automatic transmission is disabled. Repair after this type of failure is a fairly expensive procedure which requires replacement of the clutch drum at a minimum.
The device of this invention is utilizable to easily modify an automatic transmission having a configuration such as that of the turbo hydra-matic 350 transmission to prevent failure of the check ball. The applicant's device relocates the hole and check ball within the clutch piston. The new hole is drilled and fitted with a check ball and seat apparatus which is more durable in construction than the staked-in check ball utilized by existing automatic transmissions such as the turbo hydra-matic 350 transmission. The replacement check ball and seat are less likely to fail. Furthermore, if failure should occur, the repair of the transmission will require replacement of the clutch piston rather than the clutch drum. Replacement of the clutch piston is a less expensive procedure than replacement of a clutch drum.
The following prior art reflects the state of the art of which applicant is aware and is included herewith to discharge applicant's acknowledged duty to disclose relevant prior art. It is stipulated, however, that none of these references teach singly nor render obvious when considered in any conceivable combination the nexus of the instant invention as disclosed in greater detail hereinafter and as particularly claimed.
______________________________________ INVENTOR U.S. PAT. NO. ISSUE DATE ______________________________________ Gerbig, S.A. 2,365,068 December 12, 1944 Dion, E. 2,471,940 May 31, 1949 Robertson, H.P. 3,280,661 October 25, 1966 Boggs, B.A. 3,743,420 October 21, 1969 Haselmo, R.D. 3,713,747 January 30, 1973 Klee et al. 4,461,603 July 24, 1984 Sommerfeld, C.A. 4,955,766 September 11, 1990 Nordstrom, E. 4,993,895 February 19, 1991 Lee, R.C. 5,056,966 October 15, 1991 Carswell, C.W. 5,069,093 December 3, 1991 OTHER PRIOR ART Arthur, Title Pertinent Pages Year ______________________________________ Transmission "Technically Speaking" Page 34 1992 Digest Motor "Domestic Trans- Page 8-1 et seq. 1986 mission Manual" ______________________________________
The patent to Sommerfeld teaches the use of a holding fixture for drilling pocket joints from wooden pieces. It includes a vise-like structure for securely holding the piece to be drilled, a guide portion which supports the drill in the desired alignment and a stepped drill bit. The device of this application is distinguishable from Sommerfeld in that, inter alia, it is specifically designed to securely hold a clutch piston of an automatic transmission. Furthermore, the device of this application is designed for use in metalworking on high precision automotive parts which require the maintenance of precise tolerances in drilling the hole. The device taught by Sommerfeld shows an angled drill bit guide which directs the drill bit against the piece to be drilled at a non-orthogonal angle. In precision metalworking this type of an angular hole is not effectively accurately drilled even with a guide for the drill bit.
The patent to Dion teaches the use of an all purpose work holder to be utilized with a drill press. The device of the instant invention is distinguishable from Dion in that it includes a drill bit guide to ensure that the hole to be drilled is precisely located without the prior art's requirement of carefully adjusting a base of the device with respect to a table of the drill press.
The article under the column entitled "Technically Speaking" in Transmission Digest, page 34 describes the hole located in the piston retainer (i.e. clutch drum) and describes the problem of blowout of a small orifice screen due to it not being staked properly in manufacture and the result involved when the screen blows out. The screen blow out problem shares similarities with the problem of check ball blow out. While this article clearly describes the problem existing in many automatic transmissions this article does not address remedies to the problem or any methods of correcting the problem as does the method disclosed by this invention.
The book Domestic Transmission Manual published by Motor teaches at Page 8-1 et seq. the use of a C3 and C4 automatic transmission by the Ford Motor Corporation. These transmissions are characterized by having check balls located within the clutch piston which parallel the same end result achieved by the device of the instant invention. However, the instant invention is distinguishable in that it is a work holder and method for modifying a transmission to have a configuration similar to that taught by Motor. Motor teaches no such modification apparatus or procedure.
The other prior art listed above but not specifically described teach other devices for various machining operations and further catalog the prior art of which the applicant is aware. These references diverge even more starkly from the references specifically distinguished above.